Question

A pencil, when dipped in water in a glass tumbler, appears to be bent at the interface of air and water. Will the pencil appear to be bent to the same extent, if instead of water we use liquids like, kerosene or turpentine? (Yes/No)

Answer 1

Hint: When light moves from one medium to another medium, speed of light changes. Here we have to compare will this change in speed of light for different liquids.

Complete step by step solution:
 This is the usual phenomenon which we observe in our daily life. If a pencil scale dipped in water, it appears to be bent. Is it actually broken? No. Then let us just think why it will appear as broken. Let us analyse the situation in detail.
When light falls on any surface either, reflection, refraction and absorption occur. Since absorption happens by very less amount, we can neglect it. When light bounces back to the same medium then it is known as reflection. If light travels from one medium to another medium, light will bend at the surface of interference. This phenomenon is known as refraction.
As light travels from one medium to another medium, if the speed of light decreases in the second medium then it is known as optically denser medium, the first medium is known as an optically rarer medium. This change in speed of light from one medium to another medium remains constant. This constant is known as a refractive index.
When light travels from one medium to another medium, let us consider light travels from air to water, there will be a change in speed of light as it enters another medium. The speed of light is more in air, as it enters the water the speed of light decreases. This is the reason behind the bending of light. This bending of light happens at the interface of two mediums. This happens whenever there will be change in medium. Hence when a pencil dipped in water in a glass tumbler, it appears to be bent if we dip in kerosene or turpentine.
But the extent of bending differs from water to kerosene or turpentine. This will depend on the optical density of the liquid.

Hence, we conclude that a pencil, when dipped in water in a glass tumbler, appears to be bent at the interface of air and water. The pencil will not appear to be bent to the same extent, if instead of water we use liquids like, kerosene or turpentine. Because the optical density is different. In other words, the refractive index of water, kerosene, and turpentine is different.

Note: Sometimes in most of the cases we think mass density and optical density both are the same. Actually, both are different. Mass density is the ratio of mass per volume. The optical density term is related to only the speed of light. Hence, both are completely different.